As one of negative-pressure-type boosters (boosters) of this type, a negative-pressure-type booster including a booster shell configured by a front shell and a rear shell and a diaphragm disposed between the front shell and the rear shell to partition the interior of the booster shell into a constant-pressure chamber (negative-pressure chamber) and a variable-pressure chamber, the constant-pressure chamber being configured to be formed between the front shell and the diaphragm and to be connected to a negative-pressure source, and the variable-pressure chamber being configured to be formed between the rear shell and the diaphragm and to be connected to the negative-pressure chamber or atmospheric air is known. For example, an example of the negative-pressure-type booster is described in the following Patent Literature 1.